1. Field of the Invention
This invention relates to digital-to-analog converters. More particularly, this invention relates to monolithic converters that are especially adapted for operation with microprocessors, such as may be used in analog control systems.
2. Description of the Prior Art
A wide variety of digital-to-analog converters have been available now for some time. Such converters frequently employ current sources which are selectively-activated in accordance with a digital input signal. U.S. Pat. No. Re. 28,633 (Pastoriza) shows one highly successful converter design of that type. A more recent design is shown in U.S. Pat. No. 3,961,326 (Craven). Digital-to-analog converters also are employed in successive-approximation analog-to-digital converters such as disclosed in U.S. application Ser. No. 931,960 (Brokaw et al); the latter converter particularly is advantageous in that it incorporates inverted mode transistor circuitry (sometimes referred to as I.sup.2 L, for "integrated injection logic"), together with bipolar transistor circuitry, on the same monolithic chip.
There have been proposals for converters especially suited for use with microprocessors, as for example described in the paper by Schoeff entitled "A Microprocessor Compatible High-Speed 8-Bit DAC", in the February, 1978, ISSCC Digest of Technical Papers, at pages 132-133.
Although many proposals have been put forward, none has provided a satisfactory converter capable of required performance, and yet suitably simple in design to be manufactured economically. Particularly, prior art designs have not provided a monolithic converter including a reference source and an amplifier to produce voltage output, all operable by a single supply, e.g. +5 volt. It is a principal object of this invention to provide solutions to the problems encountered in achieving that goal.